基于“门控”拓扑结构的多模式力色团及其高分子力化学研究

In recent years, there is great advance in the study of polymer mechanochemistry. However, the manipulation of the mechanochemical reactivities of mechanophores and the development of multiple mechano-responsiveness are still growing and very challenging. We therefore propose here the concept of a multi-modal mechanophore that has a “gated” topology and the study of its polymer mechanochemistry. Such “gated” mechanophore is composed of a mechanochromic module as the substrate moiety and a mechanically scissile module as the gate moiety whose activation threshold force f* is larger than that of the substrate moiety. First, the gate moiety can regulate the mechanochemical reactivity of the substrate moiety and improves the substrate's performance in mechanical damage sensing in polymers. Second, the gated topology and the multi-modal characteristics of the gated mehcanophore may integrate multiple useful responses such as mechanochromism, stress-relief, stress-strengthening, and self-healing in one molecular structure, which is extremely powerful for the design and development of novel multi-functional mechano-responsive materials. We will use computation and experimental studies at different length scales from molecular level to microscopic, mesoscopic and macroscopic levels to uncover the mechanisms of the gating effect of the mehcanophore and multi-modal mechanochemical reactivities of its polymers, demonstrate the structure-property relationship and discover the way to manipulate the reactivity of mehcanophore and novel mechanochemistry. It is anticipated that this project will open new avenues to polymer mechanochemistry and its applications, which is of great scientific significance.

高分子力化学研究近年来有了长足的进展，但对力色团反应活性的调控和多重力响应性的开发仍然方兴未艾且面临巨大的挑战。本项目提出一种具有“门控”拓扑结构多模式力色团的构想并研究其高分子力化学。其中，拟分别以一个力致变色模块和一个力致可断裂模块作为底物和门控构建门控力色团，门控模块的力活化阈值f*大于底物模块；首先，拟利用门控模块调节底物模块的力化学反应活性，使底物更好地发挥对聚合物的应力破坏示警作用；再者，拟通过门控力色团的设计及其多模式特性在一个分子结构中整合力致变色、应力消除、力致增强和自修复等多种功能，开发具有多重力响应功能的聚合物材料。通过理论计算以及分子水平、微观/宏观多尺度、多层次上的研究，揭示门控多模式力色团及其高分子力化学的反应机理，探明结构与性能之间的关系，探索调控力色团反应性和崭新力化学原理的途径。本项目工作有望拓展高分子力化学的研究思路和应用范围，具有重要的科学意义。

通过本基金项目支持，我们合成了一系列新的力敏团，如自由基型力敏团BPID、螺噁嗪、二苯基环丁烯等。通过宏观拉伸实验，研究了自由基型力敏团BPID及其高分子的力致响应；通过超声和宏观拉伸等研究了螺噁嗪及其高分子的力致响应；通过超声和单分子力谱实验以及理论计算研究了二苯基环丁烯力敏团及其高分子的力化学。我们还通过单分子力谱研究了螺噻喃及其高分子的力化学、可逆性和力致逆环化后的点击反应。我们还通过单分子电导实验和理论计算研究了螺吡喃衍生物的力致逆环化的结构。基于课题组其他力敏团及其高分子力化学的研究成果，我们提出一种分子间级联反应，即利用具有更高的应力阈值下力致活化的蒽/马来酰亚胺加合物，对力致交联的阈值提高了约1nN，有利于将力致交联限制在受力更严重的区域，从而达到了分子间的门控作用，为门控机理提供了新思路。我们还发展了一种新型的门控多模式力敏团，通过肉桂酸二聚体对二苯基环丁烯进行门控，实现了多级力响应、储存链释放和应力消除。相关工作发表与Angew、JACS等期刊。